The present invention relates to a protective shield for use with a gaseous-diffusion welding head wherein the shield may be readily shaped to conform to the contour of the welded parts, or to the contour of the desired weld bead. The invention also encompasses a method of utilizing such a protective shield.
In the welding of exotic metal parts, such as those made from titanium alloys or nickelbased super alloys used for aircraft engine parts, it is necessary to use such well-known welding techniques as TIG (tungsten inert gas), plasma arc or laser beam welding. When welding these metallic alloys, it is necessary to protect the molten metal in the welding zone and the weld bead from oxidation by the surrounding atmosphere. This is achieved by directing a protective gas over these areas, the gas being an inert gas such as argon or helium.
It is well known in the art to provide such a protective gas in the vicinity of the molten metal near the welding head by directing the gas through an annular collar attached to the welding head until the weld bead has sufficiently cooled. However, it is often also necessary to prevent the oxidation of the weld bead immediately downstream of the welding head until the weld bead has sufficiently cooled. Protective shields have been proposed to accomplish this which may be attached to the welding head and be supplied with the protective gas. The shields direct the protective gas onto the weld bead to prevent its oxidation during the cooling process. In order to effectively apply the protective gas to the weld bead area, it is necessary for the protective shield to closely match the contour or the geometry of the welded parts and/or welded bead, and it must travel along with the weld head during the welding process.
The thicker are the parts to be welded, the more sensitive the welded bead is to oxidation. This requires the length of the shield to be longer in order to provide the protection of the protective gas during cooling. In titanium based parts approximately 8 mm thick, the shield may typically exceed 150 mm.
The known protective shields typically have a fixed configuration, thereby rendering them usable only with a part having a similar configuration. Each part having a different contour requires a different fixed protective shield.
Protective shields are known which may be capable of being shaped by hand, but these are difficult to form in the exact shape of the parts being welded.
Also, it has proven exceedingly difficult to utilize the known devices with fully automatic welding machines, such as robots, without limiting the capabilities of such devices.